Methods for reading a feature pattern from a packaged die

ABSTRACT

Methods for tracking the identity of die after singulation from a wafer. The product chips and die include a pattern of features formed in a metallization level of a back-end-of-line (BEOL) wiring structure. The features in the pattern contain information relating to the die, such as a unique identifier that includes a wafer identification used to fabricate the die and a product chip location for the die on a wafer. The features may be imaged with the assistance of a beam of electromagnetic radiation that penetrates into a packaged die and is altered by the presence of the features in a way that promotes imaging.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/193,825,filed Aug. 19, 2008, which is hereby incorporated by reference herein inits entirety for all purposes.

BACKGROUND

The invention relates generally to integrated circuit fabrication and,in particular, to product chips and die with a feature pattern thatcontains information relating to the product chip, methods forfabricating product chips containing the information, and methods forreading the information from the packaged die.

Product chips, which are built using a semiconductor wafer, are usuallymuch smaller than the wafer. In fact, as many as dozens of chips up totens of thousands of product chips may be fabricated using a singlewafer. The actual number of product chips yielded from a wafer is afunction of the wafer size, as well as the individual chip size. Wafermanufacturers typically mark bare wafers, usually by laser impingement,with a code or identifier at a particular location around the waferedge. The identification code, which is unique to each wafer, may behuman-readable, machine-readable, or both. Hence, at the wafermanufacturer level, the smallest trackable physical unit is usually thewafer.

At the foundry, a series of processes used to fabricate integratedcircuits or product chips containing device structures, such as fieldeffect transistors, use the wafer as a foundation. Product chips arefabricated in parallel across the surface area of the wafer in repeatingpatterns using a set of masks to replicate the device structures. Duringcertain steps of the chip fabrication process, measurements made onmanufacturing equipment may be traceable at some level to the uniquewafer identification code applied by the wafer manufacturer. At theconclusion of the fabrication process, the individual product chips aresingulated (i.e., separated from each other) using a dicing operationthat yields a corresponding plurality of die. Kerf or scribe-linechannels are reserved as product dead space between the product chipsfor the purpose of singulation. A mechanical or laser apparatus cuts orscribes the wafer along the scribe-line channels to physically singulatethe product chips into die.

Unfortunately, after physical separation from the wafer, the varioussingulated die are separated from the unique wafer identification codeassigned by the wafer manufacturer. Hence, the parent wafer of origin isno longer identifiable for the product chips. In addition, theparticular position of any arbitrary product chip in the array ofproduct chips on a wafer is lost. This complete loss of identity may beaccepted as a natural consequence of the singulation process.

Conventionally, however, special provisions may be made to retain all orpart of the identity of each singulated die. In this regard, oneconventional approach for retaining the die identity is to sequence thedie by hand, which maintains the position-on-the-wafer information.However, manual tracking is error prone and, furthermore, is costly andtime consuming with a low confidence of success in an actualmanufacturing environment. Another conventional approach is to partitiononly a single wafer in a wafer lot and/or module lot, which may not bepractical given floor control and other hardware tracking methodologies,equipment, and regulations.

Another approach is to laser scribe the backside of the chip with anidentifier similar to the identifier applied by wafer manufacturers tomark bare wafers. However, laser scribing involves additional time andexpense and is prohibited if the chip backside is to be altered byadditional chemical or mechanical processing. Furthermore, when a die isencased in a plastic or other material package, then the laser-scribedidentifier is no longer visible. A destructive de-packaging operationmay be able to recover the information by making the identifier visible.However, de-packaging may prohibit continued use of the die.

Electrical Chip Identification (ECID) represents another conventionalapproach for retaining the identity of a product chip after singulation.In ECID, a bank of fuses is blown by application of a high voltage togenerate an identifier. The configuration of the blown fuses may beelectrically read to retrieve the identifier from the die. This approachis rather expensive in terms of the amount of chip real estate consumedfor the fuses, which cannot be used to fabricate devices of theintegrated circuit product. Moreover, the fuse blowing operation is timeintensive and may result in yield losses. As chip dimensions shrink, thereal estate available for both standard chip marking and, to a lesserextent, non-destructive ECID becomes smaller as well.

What is needed, therefore, are improved methods for associatinginformation, such as a unique identifier, with die and product chips fortracking purposes after singulation from the wafer, as well as improvedmethods of nondestructively and non-invasively reading information, suchas a unique identifier, from a product chip or die, and product chipsand die carrying information, such as a unique identifier, that can beexternally read in a non-destructive and non-invasive manner from theexterior of a product package.

SUMMARY

In an embodiment of the invention, a structure includes a die having anintegrated circuit with a back-end-of-line (BEOL) wiring structure andat least one active device connected with the BEOL wiring structure. Apattern of features is included in a metallization level of the BEOLwiring structure. The features in the pattern contain informationrelating to the die. In one embodiment, the information represented bythe features of the pattern may be a unique identifier that includes awafer identification for a wafer used to fabricate the die and a productchip location for the die on the wafer.

In another embodiment of the invention, a method is provided forfabricating a product chip on a wafer. The method includes forming anintegrated circuit using the wafer and forming a back-end-of-line (BEOL)wiring structure that includes a metallization level, which is connectedwith at least one active device of the integrated circuit. The methodfurther includes forming a pattern with a plurality of featurescontaining information relating to the product chip in the metallizationlevel of the BEOL wiring structure.

In another embodiment of the invention, a method is provided for readinginformation stored as a pattern of features in a metallization level ofa back-end-of-line (BEOL) wiring structure carried on a packaged die.The method includes nondestructively directing a beam of penetratingelectromagnetic radiation into the packaged die and acquiring an imageof the pattern of features from a portion of the beam influenced by thefeatures.

The pattern of features provides the ability to uniquely identifyindividual product chips and die for the purpose of permanenttraceability. In one embodiment, the pattern of features may have theform of an identifier or serial number that can be encoded with relevantinformation for the integrated circuit manufacturer. The permanentidentification of individual product chips with the pattern of featuresmay improve current methods of quality control, failure analysis, andinventory control. In particular, the pattern of features will permitmanufacturers to more easily trace fabrication problems to their source,which may be especially acute for die that fail after packaging and arereturned to the manufacturer for failure analysis. With the benefit ofthe pattern of features, failure analysis data can be tied back to aparticular lot or batch, a particular wafer, and/or a position of aproduct chip within a wafer. Identifying the root cause of product chipfailures can enhance process control.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments of theinvention and, together with a general description of the inventiongiven above and the detailed description of the embodiments given below,serve to explain the embodiments of the invention.

FIG. 1 is a diagrammatic top view of a wafer carrying multiple productchips in accordance with an embodiment of the invention.

FIGS. 2-5 are diagrammatic cross-sectional views of a portion of one ofthe product chips in FIG. 1 illustrating successive stages of afabrication process forming a readable pattern in a back-end-of-linemetallization level in accordance with an embodiment of the invention.

FIG. 6 is a schematic perspective view depicting the use of a stream ofdroplets of a positive resist solvent to form the resist openings inFIG. 3 for use in making the readable pattern.

FIG. 6A is a schematic perspective view similar to FIG. 6 in which thereadable pattern has been formed in a dielectric layer of the involvedmetallization level.

FIG. 7 is a schematic perspective view similar to FIG. 6 depicting theuse of the stream of positive resist solvent droplets to form resistfeatures for a readable pattern in accordance with an alternativeembodiment of the invention.

FIG. 7A is a schematic perspective view similar to FIG. 7 in which thereadable pattern of the alternative embodiment has been formed in themetallization for a dielectric layer of the involved metallizationlevel.

FIG. 8 is a diagrammatic perspective view in partial cross-section of anembodiment of a writing system configured to dispense positive resistsolvent, as shown in FIGS. 6 and 7, to form the resist features.

FIG. 9 is a block diagram of an exemplary hardware and softwareenvironment for a controller suitable for interfacing with the writingsystem in FIG. 8.

FIG. 10 is a diagrammatic perspective view of an acoustic microscopethat may be used to read the information embedded in theback-end-of-line metallization level of a package including a diesingulated as one of the product chips from the wafer of FIG. 1.

DETAILED DESCRIPTION

With reference to FIG. 1 and in accordance with an embodiment of theinvention, a wafer 10 includes a front side 11 (FIG. 2) that has beenprocessed by front-end-of-line processes to fabricate a plurality ofsubstantially identical product chips 12. Each product chip 12 includesone or more integrated circuits that contain device structures, such asa representative device 14 (FIG. 2). The product chips 12 are arrangedin an array of rows and columns within the outer periphery of the wafer10. The number of product chips 12 may range from approximately ten toup to tens of thousands of chips. Among other factors, the actual numberof product chips 12 yielded from wafer 10 is a function of theindividual chip size, as well as the wafer size. Scribe-line channels 15are present between adjacent pairs of product chips 12 in the array. Thescribe-line channels 15 are free of device structures of the integratedcircuit, but may contain test devices used to evaluate post-fabricationcircuit quality.

Wafer 10 may be any suitable substrate containing a semiconductormaterial that a person having ordinary skill in the art would recognizeas suitable for forming an integrated circuit. For example, the wafer 10may be composed of a monocrystalline silicon-containing material, suchas bulk or SOI single crystal silicon. The semiconductor materialconstituting wafer 10 may be lightly doped with an impurity to alter itselectrical properties. Specifically, the wafer 10 may be lightly dopedwith an n-type impurity species to render it initially n-type or lightlydoped with a p-type impurity species to render it initially p-type.Standard round wafer sizes for wafer 10 range from a diameter of 100 mmto a diameter of 300 mm. The wafer 10 also includes a back side 13 (FIG.8) that is connected to the front side 11 by a peripheral edge 17.

With reference to FIG. 2, the devices on the wafer 10, such as therepresentative device 14, are coupled by contacts 16 in a dielectriclayer 18 and wires 20 in a dielectric layer 22 of a local interconnectmetallization level (M1 level) with each other and with the overlyingmetallization levels (M2 level, M3 level, M4 level, etc.) of aback-end-of-line (BEOL) wiring structure, which is generally indicatedby reference numeral 24. Typical constructions for the BEOL wiringstructure 24 consist of about two (2) to about eight (8) metallizationlevels. In the representative embodiment, the M4 level constitutes theuppermost level in the BEOL wiring structure 24. The local interconnectmetallization level and each of the overlying metallization levels ofthe BEOL wiring structure 24 are formed by known lithography and etchingtechniques characteristic of damascene processes conventionallyassociated with BEOL processing and as described below withparticularity for the M4 level.

To form the uppermost M4 level of the BEOL wiring structure 24, an etchstop layer 26 and an interlayer dielectric layer 28 are applied on a topsurface of the M3 level by a conventional deposition techniquerecognized by a person having ordinary skill in the art. The etch stoplayer 26 is disposed as a cap on the underlying M3 level. The etch stoplayer 26 may be formed from any dielectric material that etchesselectively to the dielectric material forming the dielectric layer 28.For example, the etch stop layer 26 may be a thin film composed ofsilicon nitride (Si₃N₄), silicon carbonitride (SiCN), siliconoxycarbonitride (SiOCN), or silicon carbide (SiC) deposited by, forexample, plasma enhanced chemical vapor deposition (PECVD).

Dielectric layer 28 may comprise any suitable organic or inorganicdielectric material recognized by a person having ordinary skill in theart. Candidate inorganic dielectric materials for dielectric layer 28may include, but are not limited to, silicon dioxide, fluorine-dopedsilicon glass (FSG), and combinations of these dielectric materials.Alternatively, the dielectric material constituting dielectric layer 28may be characterized by a relative permittivity or dielectric constantsmaller than the dielectric constant of silicon dioxide, which is about3.9. Candidate low-k dielectric materials for dielectric layer 28include, but are not limited to, porous and nonporous spun-on organiclow-k dielectrics, such as spin-on spun-on aromatic thermoset polymerresins like polyarylenes, porous and nonporous inorganic low-kdielectrics, such as organosilicate glasses, hydrogen-enriched siliconoxycarbide (SiCOH), and carbon-doped oxides, and combinations of theseand other organic and inorganic dielectrics. If the dielectric layer 28is composed of a low-k dielectric material, the physical and materialproperties of etch stop layer 26 may be adjusted so that layer 26operates as a barrier film that optimizes resist poisoningcharacteristics. Dielectric layer 28 may be deposited by any number ofwell known conventional techniques such as sputtering, spin-onapplication, chemical vapor deposition (CVD) process or a PECVD process.

A resist layer 30 composed of a radiation-sensitive organic material isapplied as a thin film to a top surface 32 of dielectric layer 28 byspin coating. The resist layer 30 is pre-baked, exposed to radiation toimpart a latent image of a via pattern, baked, and then developed with achemical developer. The chemical developer removes nonpolymerizedmaterial to transform the latent image of the via pattern in the resistlayer 30 into a final image pattern. The final image pattern imparted inthe resist layer 30 includes laterally dispersed openings 34. Each ofthe openings 34 defines a window that reveals a distinct surface area ofdielectric layer 28. Procedures for applying and lithographicallypatterning the resist layer 30 using a photomask and lithography toolare known to a person having ordinary skill in the art.

In an alternative embodiment, a hardmask (not shown) of a conventionalsingle layer or multilayer construction may applied to the top surface32 of the dielectric layer 28 before the resist layer 30. In subsequentpatterning steps, the hardmask is etched in conjunction with the resistlayer 30, which is removed after patterning the hardmask. The hardmaskthen serves as the primary mask for the etching process of FIG. 3.

With reference to FIG. 3 in which like reference numerals refer to likefeatures in FIG. 2 and at a subsequent fabrication stage, vias 23, 25,27 are defined in the dielectric layer 28 that extend from the topsurface 32 to the depth of a top surface of the etch stop layer 26.Specifically, the surface areas of dielectric layer 28 that are notmasked by the final image pattern of the resist layer 30 (FIG. 2) areremoved with an etching process, such as reactive ion etching (RIE),capable of producing substantially vertical sidewalls for the vias 23,25, 27. The etchant gases selectively attack areas of the dielectriclayer 28 not protected by the photoresist. After penetrating through thedielectric layer 28, the etch stop layer 26 halts the vertical progressof the etching process so that the underlying metallization in the M3level is not etched.

The vias 23, 25, 27 are distributed at various locations in thedielectric layer 28 as determined by the image pattern in the photomask.After the vias 23, 25, 27 are formed, the residual resist layer 30 isremoved from the top surface 32 of dielectric layer 28 with a wetchemical stripper or a dry oxidation-based photoresist removal techniquesuch as plasma ashing with an oxygen plasma.

Another resist layer 35 composed of a radiation-sensitive organicmaterial is applied with a spin coating process to the top surface 32 ofdielectric layer 28. Resist layer 35 is composed of a positivephotoresist that, when unexposed, is initially insoluble in aphotoresist developer. As understood by a person having ordinary skillin the art, the portion of the positive photoresist in resist layer 35that is exposed to radiation during the lithography process loseschemical stability and, as a result, becomes soluble to a photoresistdeveloper. The portion of the positive photoresist in resist layer 35that is unexposed to radiation during the lithography process remainschemically stable and, therefore, retains its insolubility when exposedto photoresist developer. The resist layer 35 originates from a liquidresist solution containing a resist resin dissolved in a solvent.

An adhesion promoter, such as hexamethyldisilazane (HMDS), may beinitially applied on the top surface of the dielectric layer 28 topromote adhesion of the resist layer 35 to the dielectric layer 28. Thespin coating process entails placing the wafer 10 on a spin coater,dispensing the liquid resist solution onto the top surface 32 ofdielectric layer 28, and operating the spin coater to rapidly spin thewafer 10. Spinning disperses the liquid resist solution supplied to thecenter of the wafer 10 radially outward by centrifugal forces to coatthe entire top surface 32 and to provide the resist layer 35 with anominally uniform thickness independent of location on the top surface32. A typical spin coating process runs at 1000 revolutions per minute(rpm) to about 5000 rpm for one minute or less and results in a physicallayer thickness between about 0.5 microns and about 2.5 microns. Theresist layer 35 is then heated in a soft baking or pre-baking process todrive off excess solvent and to promote partial solidification.

The soft-baked resist layer 35 is exposed to a pattern of radiation toimpart a latent image of a trough or trench pattern. For opticallithography, the pattern of radiation is generated using a photomask andan optical stepper of a lithography tool and then imaged onto the resistlayer 35. Regions of the resist layer 35 exposed to the radiation becomechemically less stable. Regions of the resist layer 35 that are notexposed to the radiation remain chemically stable. This chemicalmodification of the exposed regions of the resist layer 35 permitssubsequent removal by contact with a chemical developer.

For each of the product chips 12, openings 36 are provided in the resistlayer 35 in a peripheral region 38 of the BEOL wiring structure 24 thatborders one of the scribe-line channels 15 and is near one chamferedcorner 40 of a future die 92 (FIG. 10) when the product chip 12 issingulated. Device structures, such as device 14, of the integratedcircuit are not fabricated in the peripheral region 38, which leaves theperipheral region 38 as an electrically inactive, so far as the productchips 12 are concerned, and typically unused surface area of the wafer10. The peripheral region 38 is outside of the image field of the maskused to form the latent image of a trough or trench pattern. In therepresentative embodiment and after the product chips 12 are singulated,the openings 36 are located near at least one of the chamfered corners40 of each of the product chips 12, as best shown in FIG. 6. In therepresentative embodiment, the openings 36 have different widths andspacings, although the embodiments of the invention are not so limited.

As shown in FIG. 6, wetted regions 45 are formed in the positivephotoresist of resist layer 35 by precisely dispensing droplets 42 of apositive resist solvent onto selected impact locations or areas of theresist layer 35 in the peripheral region 38. As explained below, thewafer 10 is moved with a high degree of precision relative to theimpinging droplets 42 of positive resist solvent to promote theformation of the wetted regions 45. Because of a chemical reaction withthe positive resist solvent, the wetted regions 45 lose their chemicalstability so that these wetted regions become soluble when contacted bya positive photoresist developer. The wetted regions 45 in the resistlayer 35 have a pattern that, in a subsequent stage of the fabricationprocess, is correlated spatially with openings 36 and a feature pattern85 (FIG. 5) of metallization in the dielectric layer 28.

The positive resist solvent may be any organic solvent or mixture oforganic solvents capable of dissolving the resist layer 35 upon contactor capable of chemically destabilizing the resist layer 35 so thatexposure to the developer can form the openings. Candidate inorganicsubstances for the positive resist solvent include, but are not limitedto, toluene, xylene, a ketone such as acetone, a polyhydric alcohol suchas ethylene glycol, a cyclic ether such as dioxane, or an ester such asmethyl acetate, ethyl acetate, or butyl acetate.

The resist layer 35 may be subjected to a post-exposure bake processbefore the developing process. The elevated temperature of thepost-exposure bake process drives photoproduct diffusion in the resistlayer 35, minimizes the negative effects of standing waves in the resistlayer 35, and drives acid-catalyzed reactions in chemically amplifiedpositive resists.

The resist layer 35 is then developed with the use of a developer totransform the latent image into a final image pattern with openings 44characteristic of the trench pattern and openings 36 for the featurepattern 85. The openings 36, 44 in the resist layer 35 extend to thedepth of the top surface 32 of the dielectric layer 28. Laterallydispersed surface areas of dielectric layer 28 are unmasked by openings36, 44 so that the developer can locally wet the top surface 32 of thedielectric layer 28. The developer may be delivered on a spin coater ina manner similar to the delivery of the resist solution. An exemplarydeveloper commonly used to develop positive photoresist is an alkalideveloping liquid, such as tetramethylammonium hydroxide (TMAH) or amixture of TMAH and a surfactant. The resulting resist layer 35 on thewafer is then subjected to a hard-baking process, which solidifies theresidual photoresist of the patterned resist layer 35 to increasedurability and robustness.

The wetted regions 45, the openings 36, and, ultimately, the featurepattern 85 (FIG. 5) contain information that pertains to the particularproduct chip 12 on the wafer 10 to which applied. For example, thewetted regions 45, openings 36, and feature pattern 85 may provide aunique identification code for each of product chips 12. In oneembodiment, the wetted regions 45, openings 36, and feature pattern 85may include characters and/or symbols specifying, for example, a part orserial number encoding a location for a particular product chip 12 onthe wafer 10 and a wafer identification code for the wafer 10.Alternatively, the characters and/or symbols contained in the wettedregions 45, openings 36, and feature pattern 85 may include informationspecifying a company name or a chip manufacturer, or other informationsuch as a date code, a wafer lot identification code, chip history,testing data, and performance information.

The wetted regions 45, openings 36, and the features 80-84 (FIG. 5) ofthe feature pattern 85 may include fewer individual features than in therepresentative embodiment or more features than in the representativeembodiment. The wetted regions 45, openings 36, and features 80-84 may,for example, be arranged as a bar code or other type of machine readablecharacters and/or symbols.

In an alternative embodiment, data compression may be optionally used toexpand the amount of information recorded in the wetted regions 45,openings 36, and feature pattern 85. For example, wetted regions 45,openings 36, and features 80-84 may include a two-dimensional array ofidentification markings of any desired size and shape dots, charactersor any other type symbol or symbols capable of encoding information.Such high density formats for wetted regions 45, openings 36, andfeatures 80-84 are understood by those of ordinary skill in the art.Data compression of this type may be used, for example, to at leastpartially compensate for the relatively low spatial resolution ofavailable imaging techniques in comparison to the relatively highspatial resolutions achievable with photolithography techniques.

The wetted regions 45 and, ultimately, the openings 36 are formedindependently of the openings 44. As a result, the wetted regions 45 areformed independent of the mask used in conjunction with the opticalstepper to form the openings 44 in each of the product chips 12.

With reference to FIG. 4 in which like reference numerals refer to likefeatures in FIG. 3 and at a subsequent fabrication stage, wiringtrenches 46, 48, 50 are formed in the dielectric layer 28 at thelocations of the openings 44 in the patterned resist layer 35.Information trenches 52, 53, 54, 55, 56 are formed in the dielectriclayer 28 at the locations of the openings 36 in the patterned resistlayer 35. The wiring trenches 46, 48, 50 and information trenches 52-56expose the top surface 32 of the dielectric layer 28.

Specifically, trenches 46, 48, 50, 53-56 are formed by removing regionsof dielectric layer 28 that are not masked by the resist layer 35 (FIG.3) with an anisotropic etching process, such as an RIE process. Thedirectional etching process is capable of producing substantiallyvertical sidewalls for the wiring trenches 46, 48, 50 and substantiallyvertical sidewalls for the information trenches 52-56. The resist layer35 protects the masked surface areas of the dielectric layer 28 duringthe etching process. An optional bottom anti reflective coating layer(not shown) may be deposited in the vias 23, 25, 27, before the resistlayer 35 is deposited, to ensure that the etch stop layer 26 is notbreached during the trench etching process, which protects theunderlying metallization in the M3 level of the BEOL wiring structure24.

The resist layer 35 is removed from the top surface of dielectric layer28 with a wet chemical stripper or a dry oxidation-based photoresistremoval technique. The wiring trenches 46, 48, 50 and the informationtrenches 52-56 include substantially vertical sidewalls that extendpartially through the dielectric layer 28. Vias 23, 25, 27 communicatewith the wiring trenches 46, 48, 50, respectively, as well as with themetallization in the underlying M3 level of the BEOL wiring structure24.

With reference to FIG. 5 in which like reference numerals refer to likefeatures in FIG. 4 and at a subsequent fabrication stage, liner layers57, 58, 59 are applied in the vias 23, 25, 27 and the wiring trenches46, 48, 50. Liner layers 57, 58, 59 may be composed of any conductivematerial or multilayer combination of conductive materials recognized bya person having ordinary skill in the art. Liner layers 57, 58, 59 maycomprise a conductive material such as tantalum (Ta), tantalum nitride(TaN), titanium (Ti), titanium nitride (TiN), tungsten (W), ruthenium(Ru), iridium (Ir), rhodium (Rh), platinum (Pt), chromium (Cr), niobium(Nb), or another suitable conductor with material properties appropriateto operate as a diffusion barrier and an adhesion promoter for asubsequent metal plating process to fill the vias 23, 25, 27 and wiringtrenches 46, 48, 50. The liner layers 57, 58, 59 may be deposited, forexample, by conventional deposition processes well known to thoseskilled in the art, including but not limited to a physical vapordeposition (PVD) process, ionized-PVD (iPVD), ALD, plasma-assisted ALD,CVD, and PECVD.

Conductive wires 60, 62, 64 are formed in the open spaces inside thewiring trenches 46, 48, 50 and conductive studs 66, 68, 70 are formed inthe open spaces inside the vias 23, 25, 27. Conductive wires 60, 62, 64and conductive studs 66, 68, 70 are composed of a conductor such ascopper (Cu), aluminum (Al), alloys of these primary metals such as AlCu,W, and other similar metals. The conductor is deposited as a blanketlayer by conventional deposition processes, such as CVD, PECVD, anelectrochemical process such as electroplating or electroless plating,chemical solution deposition, PVD, DC or RF sputtering, and the like. Athin seed layer (not shown) may be deposited inside the vias 23, 25, 27and wiring trenches 46, 48, 50 to promote the deposition process. Afterthe blanket deposition, portions of the conductor fill the vias 23, 25,27 and wiring trenches 46, 48, 50 and cover the field of the dielectriclayer 28. A chemical-mechanical polishing (CMP) process is employed toremove excess conductor from the field of the dielectric layer 28 and toplanarize a top surface 69 of the dielectric layer 28 and embeddedconductive wires 60, 62, 64.

The conductive wires 62, 64 and conductive studs 68, 70 are replicatedin the underlying M1, M2 and M3 levels of the BEOL wiring structure 24.As best shown in FIGS. 5 and 6, the stacked conductive wire 64 and studs70 in the different metallization levels define a crack stop region,which is generally indicated by reference numeral 72. The crack stopregion 72 is disposed adjacent to the peripheral region 38 and defines aboundary generally between an active circuit region 74 of each productchip 12 and one of the scribe-line channels 15. The crack stop region 72functions to prevent the propagation of cracks, which are initiated bychipping and cracking formed along peripheral edges of the product chip12 during a subsequent dicing operation, into the active circuit region74 of each product chip 12. Similarly, the stacked conductive wires 64and studs 70 in the different metallization levels define a moisturebarrier or edge seal, which is generally indicated by reference numeral76, located between the crack stop region 72 and one of the scribe-linechannels 15. The crack stop region 72 is proximate to the physicalperipheral edge of each of the product chip 12 following singulation.

The conductive wires 60 and conductive studs 66 are also replicated inthe underlying M1, M2 and M3 levels of the BEOL wiring structure 24 butlack the uniformity in construction characteristic of the crack stopregion 72 and edge seal 76. Specifically, the conductive wires 60 andconductive studs 66 are routed and placed to efficiently interconnectthe devices 14 of the integrated circuit on each product chip 12 and toprovide circuit-to-circuit connections, and may also establish contactswith input and output terminals of each product chip 12.

Portions of the conductor used to form the conductive wires 60, 62, 64and conductive studs 66, 68, 70 and/or portions of the conductor used toform the liner layers 57, 58, 59 fill the information trenches 52-56 todefine features 80, 81, 82, 83, 84 of a feature pattern 85 in thedielectric layer 28. The feature pattern 85 is arranged and configuredto be read by a machine and converted to retrieve the encodedinformation. The feature pattern 85 is located in the unused peripheralregion 38 on the front side of each product chip 12 and outside of thecrack stop region 72 in what defines, after singulation into die, thechamfered corner 40.

In the representative embodiment, the feature pattern 85 is located inthe M4 level that constitutes the uppermost metallization level in theBEOL wiring structure 24. However, in an alternative embodiment, thefeature pattern 85 may be located in a different metallization levelthat happens to represent the uppermost metallization level if the BEOLwiring structure 24 includes more than four levels or less than fourlevels. In other alternative embodiments, feature pattern 85 may belocated in a metallization level that is not the topmost level so longas the feature pattern 85 is capable of being imaged.

The conductive wires 60, 62, 64 and conductive studs 66, 68, 70 form adual-damascene structure formed by a via-first, trench-last processsequence. In an alternative embodiment, the vias 23, 25, 27 and thewiring trenches 46, 48, 50 may be formed with a trough-first, via-lastdual-damascene process. The ability to perform dual damascene processsteps regardless of order is familiar to a person having ordinary skillin the art. In yet another alternative embodiment consistent with asingle-damascene process, the vias 23, 25, 27 may be formed in a lowerportion of the dielectric layer 28 and filled with a conductor, and thenthe wiring trenches 46, 48, 50 may be formed in an upper portion of thedielectric layer 28 and filled with a conductor. In either alternativeembodiment, the information trenches 52-56 are concurrently formed inthe dielectric layer 28 along with wiring trenches 46, 48, 50.

A passivation layer (not shown) of an organic polymer, such aspolyimide, or another suitable material is formed over the M4 level. Thepassivation layer includes openings that expose bond pads and probe padsat other locations in the M4 level.

Each of the product chips 12 is ultimately singulated from the wafer 10to form a discrete die 92 (FIG. 10). Each die 92 is individually housedinside a package 94 (FIG. 10), or housed with other die in a multi-chippackage, to define a packaged die 95 (FIG. 10) that is configured withexternal leads for either socket mount or surface mount on a printedcircuit board. The package 94, which encapsulates and surrounds the die92 with a layer of a cured polymer resin or plastic, such as anon-conductive epoxy, or a layer of a ceramic material, connects pads onthe die 92 to external pins of the package 94, which are connected withthe printed circuit board using the leads. The package 94 is interposedbetween the feature pattern 85 and an exterior observer of the packageddie 95. In one embodiment, the package 94 is composed of a materialcapable of permitting the propagation of sound waves with limitedattenuation.

The resulting integrated circuit chips 12 can be distributed by afabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip 12 is then integrated withother chips, discrete circuit elements, and/or other signal processingdevices as part of either (a) an intermediate product, such as amotherboard, or (b) an end product. The end product can be any productthat includes integrated circuit chips, ranging from toys and otherlow-end applications to advanced computer products having a display, akeyboard or other input device, and a central processor.

With reference to FIGS. 7 and 7A and in accordance with an alternativeembodiment of the invention, a feature pattern 85 a (7A) similar tofeature pattern 85 (FIG. 6A) may further include features, such as therepresentative characters 88, 89 (FIG. 7A). The characters 88, 89 areconfigured to be imaged and directly read by a human in an image of thefeature pattern 85 a. The characters 88, 89 may be used in combinationwith the features 80-84 of feature pattern 85, as shown in thisembodiment, or may be used alone without features 80-84. The characters88, 89 may be arranged and configured to form words, word portions,abbreviations, symbols, or other text capable of being read andcomprehended by a human. In one embodiment, the characters 88, 89 arealphanumeric characters that form a portion of a part or serial number,optionally along with other characters (not shown), encoding a locationfor a particular product chip 12 on a wafer 10 and a waferidentification code. If the characters 88, 89 have a plain text format,the information may be interpreted without any type of data translation.

To generate the characters 88, 89, additional wetted regions 90, 91(FIG. 7) are formed in the resist layer 35 that are similar to theopenings 36 (FIGS. 3, 6) at the time that the wetted regions 36 areformed. Eventually, the pattern of wetted regions 90, 91 is developedinto openings (not shown) like openings 36 (FIG. 4) and transferred byetching, when the information trenches 52-56 (FIG. 4) are etched, todefine additional information trenches. The information trenches 52-56and the information trenches used to form the characters 88, 89 areultimately filled with portions of a conductor in the damascene processto define the feature pattern 85 a.

With reference to FIGS. 8 and 9 in which like reference numerals referto like features in FIGS. 1-7, a representative embodiment of a writingsystem 100 is depicted that is capable of forming the wetted regions 45,as well as wetted regions 90, in the resist layer 35 in the peripheralregion 38 proximate to the scribe-line channel 15 on each of the productchips 12, as described above in the context of FIG. 3. The writingsystem 100 relies on a piezoelectric jet 102 to dispense the positiveresist solvent directly on the wafer 10. The piezoelectric jet 102includes a head 104 with a reservoir or chamber 106 that containspositive resist solvent 108, a developer supply 110 that is in fluidcommunication with the chamber 106, and a nozzle 112 defining anejection path in the head 104 for amounts of the positive resistdeveloper from the chamber 106. The developer supply 110 is used tocontinuously replenish the volume of positive resist solvent confinedwithin the chamber 106 as amounts of solvent are serially ejected by thepiezoelectric jet 102 from the nozzle 112 in the head 104.

The piezoelectric jet 102 further includes a piezoelectric element 114that communicates with the solvent-filled chamber 106. The piezoelectricelement 114 is composed of a material that exhibits a markedpiezoelectric effect. When potential difference is applied by a driver116 to the piezoelectric element 114, the piezoelectric material of thepiezoelectric element 114 changes shape or size, which generates apressure pulse in the positive resist solvent within the chamber 106 andforces an amount of positive resist solvent from the chamber 106 throughthe nozzle 112. Each ejected amount coalesces into one of the droplets42 after ejection from the nozzle 112. Repeatedly applying and removingthe potential difference generates a series of droplets 42 that impingethe resist layer 35.

The head 104 of the writing system 100 may include a droplet energizingelement that operates by a different type of dispensing mechanism thatis capable of ejecting droplets 42 of the positive resist solvent fromthe nozzle 112. Rather than piezoelectric actuation, for example, aheating element (not shown) could be substituted for the piezoelectricelement 114 to heat the positive photoresist solvent in the chamber 106to a point that it boils and ejects solvent from the nozzle 112 becauseof the expansion of the resultant gas bubbles. Alternatively, amagnetostrictive actuator may be used as a droplet energizing mechanismin some instances.

Alternatively, the head 104 may be equipped with multiple nozzles eachcapable of ejecting a discrete droplet of positive resist solvent.Typically, each nozzle will have associated therewith a dropletenergizing element, such as piezoelectric element 114. Alternatively, asingle droplet energizing element may be coupled with all nozzles inparallel.

The writing system 100 further includes a wafer table 120 configured tosupport and move the wafer 10. The wafer table 120 includes a firstwafer stage 122 configured to move the wafer 10 in one direction (forexample, an X direction) within a plane and a second wafer stage 124configured to move the wafer 10 in another direction (for example, a Ydirection) within the plane. Typically, the two motion directions areorthogonal to each other. For example, the X-direction may be front toback and the Y-direction may be left to right in a representativereference frame. The writing system 100 further includes motors 126, 128that, when energized, are used to respectively move the wafer stages122, 124. The wafer table 120 is configured to be moved very preciselyin a plane containing the X and Y directions by a drive mechanism suchas worm screws driven by the motors 126, 128 or by motors 126, 128 thathave the form of linear motors and slides.

The writing system 100 includes motor interface electronics 130 forcontrolling the motors and a controller 132 used to coordinate theoperation of the motors 126, 128 and the action of the piezoelectric jet102. The controller 132 is also connected with the driver 116 for thepiezoelectric element 114 so that the operation of the wafer table 120is coordinated with the operation of the piezoelectric jet 102. Themotor interface electronics 130 links the controller 132 with the motors126, 128 and translates movement commands from the controller 132 intoanalog instructions for the motors 126, 128.

A vision system 134, which is also connected with the controller 132, isused to visually image the surface of the resist layer 35. The visionsystem 134 is aimed with a field-of-view that includes all or a portionof the range of travel for the wafer table 120. In a conventional visionsystem, the vision system 134 includes a camera configured to capturepixilated gray-scale or color images of all or a portion of the wafer 10and communicate image data as a stream of electrical or optical signalsto the controller 132. The controller 132 is configured with imageanalysis software used to analyze features in acquired images.

In use, the wafer table 120 of the writing system 100 is employed toindex the wafer 10 in a controlled manner so that the feature pattern 85is applied to the resist layer 35 on each of the product chips 12 on thewafer 10. Specifically, the wafer 10 is aligned by identifying alignmentmarks (not shown) on the wafer 10 and, optionally, wafer stage marksusing one or more images acquired with the vision system 134. The wafertable 120 is operated to move the wafer 10 so that the peripheral region38 is located in a working relationship with the piezoelectric jet 102of the writing system 100. The controller 132 sends instructions throughthe motor interface electronics 130 to energize the motors 126, 128 forindexing the wafer stages 122, 124 in a two-dimensional pattern. Theindexing may be performed in discrete increments or may comprisecontinuous motion. The piezoelectric jet 102 is operated by thecontroller 132 to deliver the droplets 42 of positive resist solvent forforming wetted regions 45.

As the droplets 42 are serially delivered to the resist layer 35, themotors 126, 128 are operated by the controller 132 to drive the stages122, 124 in a motion pattern based upon the desired pattern of thewetted regions 45. The motion causes the droplets 42 to be delivered ina desired feature pattern effective to form the wetted regions 45subsequently used to etch the information trenches 52-56 in dielectriclayer 28. The droplets 42 attach themselves to the resist layer 35through a wetting action and proceed to locally modify the chemicalstability of the resist layer. A shield (not shown) may be required torestrict splashed solvent or solvent overspray from reaching activecircuit region 74.

The controller 132 may cause the wafer stage 122 to move the wafer 10and the piezoelectric jet 102 to eject droplets 42 of the solvent sothat the wetted regions 45 are directly written into the peripheralregion 38. At suitable instants in time of the piezoelectric jet 102,the controller 132 sends a control signal to the driver 116 to triggerthe piezoelectric element 114. Each trigger control signal causes thepiezoelectric jet 102 to eject one of the droplets 42 of the positiveresist solvent from the nozzle 112 in the head 104. When the wafer 10 isin an appropriate position, taking into account the time it takes forany droplet 42 to travel from the nozzle 112 to the wafer 10, thevelocity, if any, at which the wafer 10 is moving, and other factors,individual droplets 42 are ejected from the nozzle 112. Depending on thepattern to be printed, soon thereafter, another droplet 42 may beejected, and another, and a whole group of droplets 42. Time delaysbetween the ejection of consecutive droplets 42 is dependent on thepattern to be printed, the velocity of wafer motion, etc. Thus, when thewriting system 100 is nominally printing, there are time periods duringwhich one of the droplets 42 is being ejected from the nozzle 112, andtime periods during which no droplet 42 is being ejected.

Alternatively, the controller 132 may cause the wafer stage 122 to movethe wafer 10 so that the peripheral region 38 passes in a series oflinear passes of a raster pattern beneath the piezoelectric jet 102. Atsuitable instants in time of the piezoelectric jet 102, the controller132 sends a control signal to the driver 116 to trigger thepiezoelectric element 114. At the end of each linear pass, thecontroller 132 causes the wafer stage 122 to adjust the spatial positionof the wafer 10 perpendicular to the travel axis of wafer stage 124before initiating a new linear pass. The wafer stages 122, 124 of thewriting system 100 continue to move the wafer 10 in successive linearpasses until the wetted regions 45 have been fully formed.

The positive resist solvent is discharged so that the droplets 42, aftercontacting and attaching to the resist layer 35, form continuous wettedregions 45 of photoresist on different surface areas of the resist layer35 that reflect the openings 36. The solvent penetrates into thepositive photoresist within these wetted regions 45. Gaps are maintainedbetween adjacent wetted regions 45 so that, after developing, regions ofthe positive photoresist remain in the gaps between adjacent pairs ofopenings 36 to mask the dielectric layer 28 during the etching processthat forms the information trenches 52-56.

The resolution of the openings 36, the resolution of the ensuinginformation trenches 52-56, and the resolution of the resulting features80-84 in the feature pattern 85 may be as fine as one micron. However,finer or coarser resolutions may be desirable for the features 80-84. Ofcourse, increases in the amount of information in the feature pattern 85will generally require expansion of the chamfered corner 40 at theexpense of product real estate in the active circuit region 74.Concomitantly, finer resolutions for the feature pattern 85 may berequired as the amount of information contained in the features 80-84 isincreased to minimize the effect on the real estate of the product chip12 as the amount of information is increased. The piezoelectric jet 102may form droplets 42 with sizes as small as one (1) micron to two (2)microns, or less, and submicron resolution is available for the motionof the wafer stages 122, 124.

The writing system 100 may be a stand-alone unit in which instance thecontroller 132 is integrated into the system 100. Alternatively, thecontroller 132 may be associated with a higher-level server in theproduction line hierarchy that directs instructions to the writingsystem 100.

In either embodiment and as best shown in FIG. 9, the controller 132 mayinclude a processor 150, which may be coupled to vision system 134 andthe motor interface electronics 130, and the driver 116 for thepiezoelectric element 114 among other devices, and a memory 152 coupledwith the processor 150. Processor 150 may represent one or moreindividual processors (e.g., microprocessors), and memory 152 mayrepresent the random access memory (RAM) devices comprising the mainstorage of controller 132, as well as any supplemental levels of memory,e.g., cache memories, non-volatile or backup memories (e.g.,programmable or flash memories), read-only memories, etc. In addition,memory 152 may be considered to include memory storage physicallylocated elsewhere in controller 132, e.g., any cache memory in aprocessor 150, as well as any storage capacity used as a virtual memory,e.g., as stored on a mass storage device 154. The mass storage device154 may contain a cache or other data storage, which may include one ormore databases 156.

Controller 132 also typically receives a number of inputs and outputsfor communicating information externally. For interfacing with a user oroperator, controller 132 typically includes one or more of a userinterface 158 with various input devices, such as a keyboard, a mouse, atrackball, a joystick, a touchpad, a keypad, a stylus, and/or amicrophone, among others. Controller 132 may also include a display 160,such as a CRT monitor, an LCD display panel, and/or a speaker, amongothers, or other type of output device, such as a printer 162. Theinterface to controller 132 may also be through an external terminalconnected directly or remotely to controller 132, or through anothercomputer communicating with controller 132 via a network 164, modem, orother type of recognized communications device. Controller 132communicates on the network 164 through a network interface 166.

Controller 132 operates under the control of an operating system 168 andexecutes or otherwise relies upon various computer softwareapplications, components, programs, objects, modules, data structures,etc. In general, the routines executed to implement the embodiments ofthe invention, whether implemented as part of an operating system or aspecific application, component, program, object, module or sequence ofinstructions will be referred to herein as “computer program code”, orsimply “program code”. The computer program code typically comprises oneor more instructions that are resident at various times in variousmemory and storage devices in a computer, and that, when read andexecuted by one or more processors in a computer, causes that computerto perform the steps necessary to execute steps or elements embodyingthe various aspects of the invention.

The writing system 100 may provide a user with the ability to programthe controller 132 with instructions for the production of wettedregions 45 (FIGS. 3, 6) and/or wetted regions 90 (FIG. 7) in the resistlayer 35, which is ultimately reflected in the form of the featurepattern 85 or 85 a after the damascene process concludes. The user mayprovide instructions for the production of the wetted regions 45, 90 tothe controller 132 via the user interface 158. Alternatively, theinstructions for the production of the wetted regions 45, 90 may bereceived remotely, such as from another computer that is operativelycoupled to controller 132 through network 164, for example. The othercomputer may be, for example, the controller for a photolithographytool. The software executing on the controller 132 may be configured toautomatically assign different values to the information contained inthe feature pattern 85 or 85 a for different product chips 12.

With reference to FIG. 10, a reading apparatus in the representativeform of a scanning acoustic microscope 140 is used to image theinformation engrained in the feature pattern 85 (FIGS. 6, 6A) and/orfeature pattern 85 a (FIGS. 7, 7A) from the front side 11 of the die 92.The scanning acoustic microscope 140 is electrically coupled with atransducer 142, which is configured to emit a focused acoustic wave ofsound energy communicated to the packaged die 95 and ultimately throughthe package 94 to the die 92. The transducer 142, which is placed inproximity to the packaged die 95 when imaging the feature pattern 85,also acts as a detector for detecting the acoustic beam reflected fromthe feature pattern 85 and other structures like the crack stop region72, etc. The transducer 142 converts time-modulated electrical energyinto mechanical vibrations to generate an acoustic wave. The transducer142 may be composed of a material, such as lead zirconate titanate(PZT), that exhibits a marked piezoelectric effect and, as a result, iscapable of energy conversion by this mechanism. The scanning acousticmicroscope 140 includes a display 146 and a multi-axis stage 148 used tomove the packaged die 95 relative to the transducer 142. The display 146is configured to display an image of the information contained in thefeature pattern 85 to an observer. The multi-axis stage 148 may besimilar in construction to the wafer table 120 (FIGS. 8, 9) for thewriting system 100.

A coupling fluid 144, such as distilled water or alcohol, may be presentin a thin liquid film between the transducer 142 and the package 94. Thecoupling fluid 144 promotes efficient propagation of the ultrasoundwaves delivered to and from the die 92 and package 94.

In use, the scanning acoustic microscope 140 sends an electrical pulsetrain to the transducer 142, which converts the electrical energy intomechanical vibrations to generate an acoustic wave. The transducer 142launches the acoustic wave, which carries sound energy, as a train ofultrasonic pulses through the working fluid 144 for transmission intothe coupling fluid 144 and, subsequently, into and through the package94 and die 92. The transducer 142 also receives sound pulses reflectedfrom the product chip 12. Irregularities, such as discontinuities andother disturbances like the feature pattern 85, and/or the featurepattern 85 a, in the product chip 12, are detectable by reflectionbecause of differences in acoustical impedance produced by theirpresence. The transducer 142 transforms the reflected sound pulses intoelectromagnetic pulses and communicates the electromagnetic pulses in adata stream to the scanning acoustic microscope 140.

The scanning acoustic microscope 140 may display this informationreceived from the transducer 142 as an image on the display 146 in whichpixels have defined gray-scale values contingent upon the pulseamplitude. The images may be deduced from changes in reflected peakamplitude, time of flight, phase inversion, or other imaging techniquesfamiliar to a person having ordinary skill in the art of scanningacoustic microscopy. The scanning acoustic microscope 140 may analyzethe raw image using an image analysis program as known to one skilled inthe art.

In alternative embodiments of the invention, the reading apparatus mayrely on a scanning beam of a different type of penetratingelectromagnetic energy outside of the acoustic band in theelectromagnetic spectrum, including but not limited to infraredradiation, terahertz radiation, or x-rays. In an event, the acousticenergy or penetrating electromagnetic energy penetrates through the diepackage 94 and the die 92 nondestructively and non-invasively so thatthe feature pattern 85, 85 a carried on the die 92 can be imaged withoutdamaging the package die 95.

In an embodiment of the invention, the feature pattern 85, 85 a appliedto each of the product chips 12 on wafer 10 may be used in conjunctionwith die testing or integrated circuit failures. Armed with knowledgefrom the feature pattern 85, 85 a, any arbitrary die 92 may becorrelated with the specific location of the corresponding product chip12 on the parent wafer 10. These associations may be used to gather andtrack statistics based on a lot of wafers, a single wafer, or individualdie. The statistics may show, for example, trends in failures of partsof a particular wafer lot or a particular parent wafer location for awafer lot.

References herein to terms such as “vertical”, “horizontal”, etc. aremade by way of example, and not by way of limitation, to establish aframe of reference. The term “horizontal” as used herein is defined as aplane parallel to a conventional plane of a semiconductor substrate,regardless of its actual three-dimensional spatial orientation. The term“vertical” refers to a direction perpendicular to the horizontal, asjust defined. Terms, such as “on”, “above”, “below”, “side” (as in“sidewall”), “upper”, “lower”, “over”, “beneath”, and “under”, aredefined with respect to the horizontal plane. It is understood thatvarious other frames of reference may be employed for describing theinvention without departing from the spirit and scope of the invention.It is also understood that features of the invention are not necessarilyshown to scale in the drawings. Furthermore, to the extent that theterms “includes”, “having”, “has”, “with”, or variants thereof are usedin either the detailed description or the claims, such terms areintended to be inclusive in a manner similar to the term “comprising.”

It will be understood that when a structure is described as being“connected” or “coupled” to or with another structure, it can bedirectly connected or coupled with the other structure or, instead, oneor more intervening structures may be present. In contrast, when astructure is described as being “directly connected” or “directlycoupled” to another structure, intervening structures are present. Whena structure is described as being “indirectly connected” or “indirectlycoupled” to another structure, at least one intervening structure ispresent.

The fabrication of the structures herein has been described by aspecific order of fabrication stages and steps. However, it isunderstood that the order may differ from that described. For example,the order of two or more fabrication steps may be swapped relative tothe order shown. Moreover, two or more fabrication steps may beconducted either concurrently or with partial concurrence. In addition,various fabrication steps may be omitted and other fabrication steps maybe added. It is understood that all such variations are within the scopeof the present invention. It is also understood that features of thepresent invention are not necessarily shown to scale in the drawings.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of reading information stored as apattern of metal features in a metallization level of a back-end-of-line(BEOL) wiring structure carried on a packaged die, the methodcomprising: directing a beam of sound energy into the packaged die andtoward a peripheral region of the die between an active circuit regionand a scribe-line channel; detecting the sound energy reflected from thepattern of metal features in the peripheral region; converting thereflected sound energy into an image of the pattern of metal features;and determining the information relating to the manufacture of the diefrom the image of the pattern of metal features, wherein the metalfeatures specify at least a portion of a part number, at least a portionof a serial number, a wafer identification for a wafer used to fabricatethe die, or a product chip location for the die on the wafer.
 2. Themethod of claim 1 further comprising: displaying the image as pixels ona display.
 3. The method of claim 2 wherein the pixels are presented asgray-scale values.
 4. The method of claim 1 further comprising:generating failure analysis data from the information.
 5. The method ofclaim 4 further comprising: using the failure analysis data to associatethe die with a particular lot of wafers, a particular wafer, or aposition of a product chip within a wafer.
 6. The method of claim 1wherein the features of the pattern comprise a plurality ofmachine-readable characters or a plurality of machine-readable symbols.7. The method of claim 1 wherein the features of the pattern furthercomprise one or more characters capable of being read and comprehendedby a human.
 8. The method of claim 1 wherein the features of the patternfurther comprise alphanumeric characters.
 9. The method of claim 6wherein the machine-readable characters or the machine-readable symbolscomprise identification markings arranged in a two-dimensial array. 10.The method of claim 1 further comprising: correlating the informationwith die testing.